The DQDB protocol, described hereinafter and more fully in IEEE 802.6 Committee, "Draft of Proposed IEEE Standard 802.6 Distributed Queue Dual Bus (DQDB) Metropolitan Area Network (MAN)"--Drafts D0 to D10, is advantageous in a number of respects but it does not provide a technique by which a guaranteed capacity can be allocated to each station in a network, which is desirable if a station has to transmit delay sensitive services which require access to at least a specified number of packets per unit of time. Traffic requiring a guaranteed capacity, or bandwidth, can be either connection oriented (e.g. variable or fixed rate video requires low delay jitter) or connectionless (e.g. fast and reliable large file transfer). This type of traffic will hereinafter be referred to as guaranteed capacity traffic.
Therefore, an access protocol is required which is able to ensure guaranteed capacity and adequate performance, e.g. low delay for connection oriented services or for fast and reliable large file transfer.